import { NextResponse, type NextRequest } from "next/server";
import { LOCALE_COOKIE } from "@/src/domain/locale";
import { routeRequest } from "@/src/domain/routes";

const PERMANENT = 308;
const TEMPORARY = 307;

/**
 * Picks the language of a request and maps the public addresses onto the app
 * directory. All decisions are made in src/domain/routes.ts; this only carries
 * them out.
 */
export function proxy(request: NextRequest) {
  const decision = routeRequest({
    pathname: request.nextUrl.pathname,
    cookie: request.cookies.get(LOCALE_COOKIE)?.value,
    acceptLanguage: request.headers.get("accept-language"),
  });

  const url = request.nextUrl.clone();
  url.pathname = decision.to;
  const response =
    decision.kind === "redirect"
      ? NextResponse.redirect(url, decision.permanent ? PERMANENT : TEMPORARY)
      : NextResponse.rewrite(url);

  // The answer depends on the visitor's language: caches must keep one per language.
  if (decision.negotiated) {
    response.headers.append("Vary", "Accept-Language, Cookie");
  }
  return response;
}

export const config = {
  // Pages only: not Next's own files, the analytics and error proxies, or files.
  matcher: ["/((?!_next/|stats/|errors/|.*\\..*).*)"],
};